DelayCommandExecutor.java

public final class DelayCommandExecutor implements CommandExecutor {

    private final DelayService delayService = new DelayService();

    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        final Player player = (Player) sender;

        if(delayService.isPlayerInDelay(player)) {
            final int remainPlayerDelay = delayService.getRemainPlayerDelay(player);
            player.sendMessage(String.format("You're in delay, remain time %ss%n", remainPlayerDelay));
            return true;
        }

        //TODO: Logic here

        delayService.updatePlayerDelayToRegistry(player, 10);
        return true;
    }
}

DelayService.java

public final class DelayService {

    private final Map<String, Integer> delayRegistry;

    public DelayService() {
        this.delayRegistry = new HashMap<>();
    }

    public int getPlayerDelayFromRegistry(Player player) {
        final Integer cachedDelay = delayRegistry.get(player.getName());
        return cachedDelay != null
          ? cachedDelay
          : 0;
    }

    public void updatePlayerDelayToRegistry(Player player, int delay) {
        final int totalDelay = (int) (System.currentTimeMillis() / 1000) + delay;
        delayRegistry.put(player.getName(), totalDelay);
    }

    public int getRemainPlayerDelay(Player player) {
        final int playerDelayFromRegistry = getPlayerDelayFromRegistry(player);
        return (int) (playerDelayFromRegistry - (System.currentTimeMillis() / 1000));
    }

    public boolean isPlayerInDelay(Player player) {
        return getPlayerDelayFromRegistry(player) >= (System.currentTimeMillis() / 1000);
    }
}